Photo-electric relay comprising a dirtfree transparent enclosure for the optical elements



Dec. 20, 1966 D. R. PERCIVAL 3,293,504 PHOTO-ELECTRIC RELAY COMPRISING A DIRT-FREE TRANSPARENT ENCLOSURE FOR THE OPTICAL ELEMENTS Filed Sept. 24, 1963 INVENTOR DON R. PERRC/VAL 3 .IIA H FIG. 2.

ATTORNEY States Patent @filice 3,293,504 Patented Dec. 20, 1966 3,293 504 PHOTO-ELECTRHC RELAlK COMPRISING A DIRT- FREE TRANSPARENT ENCLOSURE FOR THE DPTECAL ELEMENTS Don R. Percival, Shrewsbury, Mass, assignor to Machinery Electrification, Inc., Northboro, Mass.,

a corporation of Massachusetts Filed Sept. 24, 1963, Ser. No. 311,120 1 Ciaim. (Cl. 317-124) This invention relates to a photo-electric relay and, more particularly, to apparatus arranged to connect or disconnect an electrical circuit in response to the intensity of light.

A cadmium selenide photo resistor is capable of offering very large changes of resistance with small changes of light intensity. These resistors have been used to operate a small relay directly in series with the cell, thus eliminating the need for a vacuum tube and amplifier as has been necessary in the past with photo-electric cells. Generally speaking, such a simple relay is operated on direct current obtained from a rectifier and a capacitor as part of the assembly. However, it is possible to eliminate the rectifier and capacitor and to operate the device on 110 volts, 60 cycle power. The circuit, then, becomes a simple series circuit of the relay coil and the photo resistor. When such a relay as previously constructed has been used in an area of substantial ambient light to read a source of illumination, substantial problems have presented themselves. For instance, the relay has ditficulty distinguishing between the background light and the source and operation has been slow and erratic. Also, dust entering the relay enclosure has had a tendency to shift the light intensity cutoff point; this becomes important when the relay is used to perform a function at the time when a predetermined intensity of illumination is reached in an area of gradually increasing or decreasing intensity, i.e., turning street lights on and off. These and other difficulties experienced With the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a photo-electric relay which may be operated in response to relatively small changes in illumination.

Another object of this invention is the provision of a photo-electric relay to be operated with a minimum of difiiculty due to accumulation of dust.

A further object of the present invention is the provision of a relay making use of a cadmium selenide photo resistor which may be operated by minimal changes of light intensity without the operating point changing due to dust accumulation.

It is another object of the instant invention to provide a relay operated by light falling on a photo resistor which operates on alternating current electricity to give quick and clean making or breaking of contact.

Another object of the invention is the provision of a photo-electric relay in which the optical elements are completely contained in a dust-free enclosure, yet which may be readily inspected without opening the enclosure.

With these and other objects in view, as will be apparent to those skilled in the art, invention resides in the combination of parts set forth in the specification and covered by the claim appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of a relay embodying the principles of the present invention;

FIG. 2 is a vertical sectional view of the relay taken on the line II-II of FIG. 1;

FIG. 3 is a vertical sectional view of a portion of the invention taken on the line III-III of FIG. 2; and

FIG. 4 is an electrical schematic view of the invention.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the relay, indicated generally by the reference numeral 10, is shown as consisting of a housing 11 in which is mounted a cadmium selenide photo resistor 12, a lens 13, and a relay element 14. The housing is formed of plastic material and was provided with a front wall 15 and a rear Wall 16 joined by a bottom wall 17. A groove 18 extends around the edges of the housing and is adapted to receive the edges of a U-shaped light-tight enclosure (not shown) but which serves to enclose all of the apparatus with the exception of the outer convex surface of the lens 13. Fastened to the rear wall 16 by means of bolts 19 is an L-shaped support 21 having a vertical portion 22 parallel to and slightly spaced from the rear wall 16 of the housing and a horizontal portion 23 which is parallel to and spaced from the bottom 17 of the housing. The front wall 15 of the housing is provided with a tubular hood 26 in which is carried a rubber O-ring 27. This ring engages a shoulder 40 in the hood and the lens 13 presses against it. The front wall 15 is provided with a tubular extension 24 which fits tightly into the bore in the hood 26 and presses firmly against the inner surface of the lens 13. Extending through the front wall 15 and the extension 24 is a bore 25 which carries a tube 20 formed of a transparent plastic material. At the end of the tube 20 opposite the end adjacent the lens 13 is mounted the photo resistor 12 and in its intermediate portion is mounted an apertured member such as a disk 28 having a small central apertur 30.

The cadmium selenide photo resistor 12 is of the wellknown type which has a low resistance when light falls on it and a high resistance when light does not fall on it. Mounted on the horizontal portion 23 of the support 21 is a sheet metal bracket 29, best shown in FIG. 3. The bracket is provided with a base portion 31 which is fastened to the upper surface of the horizontal portion 23 of the support 21. On this base portion is mounted a relay coil 32 having an iron core 33. The bracket 29 is provided with a vertical portion 34 having in the lower portion a lug 35 and in the upper portion an aperture 36. Through the aperture extends a movable element 37 of the relay. A portion of the movable element extends through the aperture 36 and overlies the lug 35; a coil spring 38 extends in tension between the two to bias the movable element 37 in an upward direction. The outer end of the movable element is provided with a vertical insulated plate 39 formed of a non-electrically conducting material. At the top of the vertical portion 34 the bracket 29 is provided with a short table portion 41 having mounted on its upper surface an insulating plate 42, a contact finger 43 having apertured electrical attachment lugs extending rearwardly therefnom, another insulating plate 44, a contact finger 45 having an electrical attachment lug extending rearwardly therefrom, an insulating plate 46, a contact finger 47 with a rearwardly-extending lug, and lastly another insulating plate 48. The central contacting finger 45 extends at its forward end through the plate 39 and moves upwardly and downwardly with the plate and with movable element 37 of the relay element. The plates and fingers are fastened to the table portion 41 by means of screws in the usual way. In its normal position with the coil 32 unenergized the spring 38 biases the movable element 37 upwardly; this causes the plate 39 to carry the central contact finger 45 into electrical contact with the upper contact finger 47; when the coil 32 is energized, however, the movable element 37 moves downwardly into contact with the core 33. This movement carries the plate 39 and the central contact finger 45 so that the last-named finger contacts the lower contact finger 43.

Referring particularly to FIG. 4, which shows the electrical connections, a line 52 is connected to one side of a source of alternating current electrioity (not shown). The other end of the line 52 is connected to one side of the photo resistor 12. The other side of the photo resistor is connected by a line 53 to one side of the coil 32 of the relay element 14. The other side of this coil is connected by a line 54 to the other side of the alternating current source. As is usual in most relays, there are binding posts to which a circuit may be connected for use as a normally-closed circuit and others which may be used as a normally-open circuit. The finger 45 and the finger 47 serve as a normally-closed portion of the relay while the finger i5 and the finger 43 serve as a normally-open portion. These fingers may be inserted in an electrical circuit to perform switching operations as desired.

The transparent tube 26 is formed in two parts: a forward portion 55 and a rearward portion 56. The forward portion has an enlargement 57 with a cylindrical surface which fits tightly in the bore 25 in the front wall and the extension 24. For most of their lengths, the forward portion 55 and the rearward portion have equal internal and external diameters and are fastened coaxially. The end of the rearward portion 56 that contacts the forward portion 55 is provided with a counterbore 58 in which the disk 28 exactly fits. At its other end, the rearward portion 56 is provided with a counterbore 59 in which fits the photo resistor 12. The aperture 3% is located at the focal point of the lens 13. The photo resistor 12, the rearward portion 56, the disk 28, the forward portion 55 and the front wall 15 (including the extension 24) are all cemented together in dust-tight relationship. Similarly, the hood 26 is cemented to the extension 24 and to the front wall, the dimensions being such that the lens 13 is pressed tightly against the O-ring 27 which, in turn, presses against the shoulder 4t and is deformed.

The operation of the invention will now be readily understood in view of the above description. With the apparatus connected to the alternating current circuit, with the closure over the housing 11, and with no light coming through the lens 13, the photo resistor 12 has a very low resistance. For that reason, no current flows through the coil 32 and the movable element 37 is in its upper position, thus closing the circuit between the finger 45 and the finger 47 and keeping open the circuit between the finger 45 and the finger 43. Whe light is admitted to the lens 13, however, it falls on the photo resistor 12 and causes its resistance to drop very rapidly. When this happens, current passes through the line 54, the coil 32, the line 53, the photo resistor 12, and the line 52. The energization of the coil 32 in this way causes an electromagnetic field to be set up around the iron core 33 and draws the movable element 37 downwardly into contact with the core. The movement of the member 37 causes a similar downward movement of the plate 39 which carries the finger 45 with it and into contact with the finger 43, thus closing that circuit and opening the circuit between the finger 45 and the finger 47.

The effect of locating the disk 28 and its aperture 30 at the focal point of the lens 13 is to assure that the general illumination around the relay has little effect on the photo resistor 12. When an intense light appears directly in line with the lens, however, it is focused directly on the aperture 3 This means that there is a maximum difiercnce in effect on the photo resistor between the general illumination on the one hand and the special light source. Therefore, there is substantially less likelihood of operation of the relay by a false source. In addition, the accumulation of dust on the surface of the photo resistor 12 would mean that a more intense light would be necessary to fire the relay; in many installations this results in a gradual drift of relay operation away from a preselected light intensity point. The present construction assures that such a dust accumulation cannot take place; nevertheless, the optical surfaces may be readily examined because of the transparent nature of the tube 20.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired, to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

A photo-electric relay, comprising a photosensitive element consisting of a cadmiuim selenide photo resistor which has a high resistance when light falls on it and a low resistance when no light falls on it, a relay coil, the element and the coil being connected in series for connection across an electric source, a movable element associated with the coil and adapted on movement to bring about a switching function, and means including a lens and an apertured member causing the light to pass in a defined path to the photosensitive element, the apertured member and the lens being joined by a tube of transparent plastic material, the apertured member consisting of a disc fastened in an intermediate portion of the tube and provided with a central aperture which is located at the focal point of the lens.

References Cited by the Examiner UNITED STATES PATENTS 2,817,021 12/1957 Williams et al. 250-234 2,913,637 11/1959 Bayley 317-124 x 3,176,196 3/1965 Dunigan 317 124 X RALPH G, NILSON, Primary Examiner.

WALTER STOLWEIN, Examiner. 

